Increased processing and connectivity capabilities of portable devices have resulted in a corresponding increase in the energy consumption of these devices. Furthermore, there are practical physical limits as to how much energy a portable device can store, thus necessitating frequent charging of these devices. Tethered solutions to powering portable devices are limited in part due to a lack of standardization of the connectors between the power cable and device, the weight and reliability of the charging cables, restrictions on the operating environment (e.g. underwater or hazardous areas), and the general constraints on mobility that tethered solutions impose.
Wireless charging of portable devices, has previously been limited to short distances (e.g. on the order of centimeters) by near-field techniques such as inductive or capacitive coupling. Far-field techniques that use lasers or microwave beams involve dangerously high power levels, particularly in an environment including humans. Lasers and microwave beams are also typically limited to line-of-sight applications.
Improvements in the capabilities of portable devices have also helped enable an environment of an Internet of Things (IoT) wherein large and dense deployments of devices could collectively share information. However, previous solutions have been limited in their ability to efficiently power devices in an IoT environment, where the devices require mobility, and have significantly different power consumption requirements. Similarly, increased usage of Radio Frequency Identification (RFID) tags requires an efficient way of powering devices in a mobile environment without tethering, using dangerously high levels of power, or imposing undue restrictions on the placement of charging stations used to charge the RFID tags.